OBJECTIVES: 1. Perfect a biological preparation which will allow independent forcing of chest volume and CO2 concentration. 2. Study how two important inputs affect the output of the central neural oscillator a. Determine the period and amplitude of the neural oscillator as a function of the static values of these two inputs b. Determine the relative importance of the two inputs (first for static values then dynamic). Express this relative importance in an equation showing so much CO2 concentration is equivalent to so much stretch. 3. Observe how hypoxia and hyperoxia affect the above relationship. 4. Block certain sets of receptors to ascertain the specific effect of the forced variable on one set (e.g. block carotid body to distinguish the effect of carotid body from intrapulmonary CO2 receptors). These experiments are intended to improve the knowledge of how the human respiratory oscillator works in health and disease. The chicken preparation is used as a model only because it affords a unique opportunity to manipulate two important sets of receptors in an awake ambulatory subject. To achieve these objectives a preparation has been designed which will allow independent, open-loop forcing of chest volume and CO2 concentration in the lungs. This study consists of applying various combinations and permutations of static, step, oscillatory and pulse functions as these two input variables and observing the effect on the frequency and amplitude of the output of the respiratory center.